1. Field of the Invention
The present invention relates to an epoxy resin composition. More specifically, it relates to an epoxy resin composition having an excellent heat resistance, weathering resistance, and water resistance, excellent compatibility with other epoxy resins, and having flexibility and an appropriate elasticity. The present epoxy resin composition is suitable for uses as, for example, adhesives, coating materials, coating compositions, potting materials, and cushioning materials.
2. Description of the Related Art
It is heretofore known in the art that the peeling strength is generally low when conventional epoxy resins are used as adhesives due to their hardness and brittleness. Since conventional epoxy resins are susceptible to cracking, they cannot be widely used as, for example, structural materials and coating materials. Furthermore, it is difficult for conventional epoxy resins to be used in the applications where both flexibility and elasticity are required (e.g., coating materials for concrete structures, cushioning materials, and potting materials for portions subjected to internal stress) due to their inherent insufficient adhesiveness.
Various attempts have been made to improve the above-mentioned disadvantages of conventional epoxy resins. For example, flexible epoxy resins have been used, which are classified into two groups; i.e., one group in which flexibility is afforded to the skeleton of epoxy resins, and the other in which flexibility is afforded to curing agents. Examples of the former type epoxy resins are glycidyl ester type, polyoxyalkylene glycol type, bisphenol A propylene oxide addition type, urethane modified type, and polybutadiene modified type epoxy resins. However, when these flexible type epoxy resins are used, the curing rate is remarkably so slow that the workability or processability thereof is poor. Furthermore, the resultant cured products exhibit plastic type elongation and, therefore, these epoxy resins are not suitable for use in the above-mentioned materials requiring elasticity. Examples of the above-mentioned flexible curing agents are polyamides (e.g., condensation products of dimeric acids or aliphatic dibasic acids with polyamides), long-chain amines (e.g., polyether amines and modified aliphatic amines), and modified liquid polybutadienes. However, problems arise in these curing agents regarding the compatibility, curing rate, and physical properties of the cured products and, therefore, are not suitable for practical use.
The use of several epoxy resins based on organopolysiloxane has also been proposed due to the facts that polymers having an organopolysiloxane skeleton have excellent characteristics in heat resistance, water resistance, and gas permeability. However, these epoxy resins are disadvantageous in that the reactivity thereof is low, that the cured products are extremely brittle, and that the compatibility thereof with other epoxy resins is poor.